Studies for S tudents. 



CONDITIONS OF SEDIMENTARY DEPOSITION. 



EROSION. 



Erosion consists of fragmental reduction and abrasion of rock 

 masses, chemical disintegration of rocks and transportation. 

 The three sub-processes may be called rock-breaking, rock-decay 

 and transportation. They are conditioned by declivity, lithologic 

 character and climate. 



ROCK-BREAKING. 



Favorable conditions : 



(ay Steep slopes. 



(b) Bare rocks. 



(c) Cleaved and jointed rocks. 



(d) Alternation of hard and soft beds. 



(e) Rapid changes of temperature. 

 (/) Aridity and high winds. 



(g) Abundant rainfall, in the absence of vegetation, 

 (/z) Sea cliffs. 

 Products: Shingle, gravel and sand of mixed mineralogical 

 composition. 



ROCK-DECAY. 



Favorable conditions : 



(a) Gentle slopes. 



(b) Porous soil. 



(c) Soluble rock constituents. 



(d) Carbonic acid and other acids of organic decay. 



(e) Abundant rainfall in the presence of vegetation. 

 ■(/) Prolonged transportation of gravel and sand. 



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